• 조명전기설비학회논문지
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• 제26권12호
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• pp.74-79
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• 2012

Currently, separated buses were increased to limit a fault currents in power transmission system. However, separated buses caused bad influences such as a decrease of reliability and stability. Superconducting fault current limiter (SFCL) was proposed to limit a fault current lately and that has many merits beside any other solutions. Therefore, we proposed the install of Superconducting fault current limiter (SFCL) in power transmission system with separated bus. And our proposal was verified by reliability of power system.

• Structural Engineering and Mechanics
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• 제71권3호
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• pp.271-282
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• 2019

The span record of cable-stayed bridges has exceeded 1,000 m, which makes research on the maximum possible span length of cable-stayed bridges an important topic in the engineering community. In this paper, span limit is discussed from two perspectives: the theoretical span limit determined by the strength-to-density ratio of the cable and girder, and the engineering span limit, which depends not only on the strength-to-density ratio of materials but also on the actual loading conditions. Closed form equations of both theoretical and engineering span limits of cable-stayed bridges determined by the cable and girder are derived and a detailed parametric analysis is conducted to assess the engineering span limit under current technical conditions. The results show that the engineering span limit of cable-stayed bridges is about 2,200 m based on materials used available today. The girder is the critical member restricting further increase in the span length; its compressive stress is the limiting factor. Approaches to increasing the engineering span limit are also presented based on the analysis results.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2003년도 춘계학술대회 논문집 전기기기 및 에너지변환시스템부문
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• pp.69-71
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• 2003

Switched reluctance machine has much attention because of high efficiency, high power and DC series torque characteristics with a traction drive. But the motor has to have a regenerative mode when it is adopted in an electric vehicle. A current divergence during the regeneration makes difficulties in the control of SRM. This paper proposes a reference current limitation strategy for a stable regeneration based on simulations and experimental tests. The motor is operated with conventional current limit and switching angle control method in motoring mode. Simulations and experiments are executed to verify proposed method.

• 전력전자학회논문지
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• 제8권3호
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• pp.285-291
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• 2003

스위치드 릴럭턴스 전동기는 고출력, 고효율 및 직권전동기 구동특성 등으로 견인구동용으로 주목받고 있다. 그러나 전동기를 4상한 구동하기 위한 발전영역에서 제어는 쉽지 않다. 본 논문은 전류제한법에 의해 안정된 발전제동이 가능한 제어방식을 제안하였다. 전동기 구동시는 기준전류제한방식과 위상각 제어방식으로 속도제어를 행하고, 발전제동모드에서는 상전류가 발산하지 않는 조건을 산정하여서 이 값을 기준전류로 한 전류제한방식을 채택하였다. 시뮬레이션과 실험에 의해 제안한 방식의 타당성을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1999년도 하계학술대회 논문집 D
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• pp.1704-1706
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• 1999

$YBa_2Cu_3O_x$ superconducting thick film was fabricated by surface diffusion process of $Y_2BaCUO_5$ and the mixed compound of $(3BaCuO_2+2CuO)$ expected to be liquid phase above the peritectic temperature of YBa2Cu30x. For the surface diffusion. 3BaCu02+2CuO mixed with binder material was patterned on $Y_2BaCuO_5$ substrate by the screen printing method. The characteristic of current limit on thick film fabricated was measured. The thick film limited the current from $2.8213mA_{rms}$ to $4.2034mA_{rms}$ with $500{\Omega}$ load resistance, and from $4.1831mA{rms}$ to $4.2150mA_{rms}$ with $10{\Omega}$ load resistance.

• 전력전자학회논문지
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• 제21권4호
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• pp.312-319
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• 2016

Zero-sequence Circulating Current (ZSCC) flows inevitably in parallel converters that share common DC and AC sources. The ZSCC commonly flowing in all converters increases loss and decreases the overall capacity of parallel converters. This paper proposes a simple and effective ZSCC suppression method based on the Space Vector PWM (SVPWM) with the ZSCC controller. The zero-sequence voltage for the proposed SVPWM is calculated on the basis of the grid voltage and not on the phase voltage references. The limit of the linear modulation region of the converters with the proposed method is analyzed and compared with other methods, thereby proving that the limit of the region can be extended with the proposed method. The effectiveness of the proposed method has been verified through the experimental setup comprising four parallel three-level converters. The ZSCC is confirmed to be well suppressed, and the linear modulation region is extended simultaneously with the proposed method. Moreover, the proposed control method does not require any communication between the converters to suppress the ZSCC unlike other conventional methods.

• 대한전기학회:학술대회논문집
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• 대한전기학회 2005년도 제36회 하계학술대회 논문집 A
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• pp.368-370
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• 2005

Due to the tendency towards large capacity and complexity of power system, an enhancement of power system equipment make a system impedance to be low in power system. Generally if an equivalent impedance of system becomes lower, a system stability will be better. But the fault current becomes very larger. The 345kV ultra-high voltage system will use current limit reactors(CLR) in a transmission line or a bus in substation to limit the magnitude of fault current. The CLR makes a significant contribution to the severity of the transient recovery voltage(TRV) experienced by feeder and bus circuit breakers on clearing feeder faults. Based on the conclusions of an investigation of actual circuit breaker failures while performing this duty, the mitigation of the transient recovery voltage associated with the reactors is described. Therefore in this article we simulated the TRV by EMTP at Bus Terminal Fault.

• 전기학회논문지
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• 제61권3호
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• pp.485-490
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• 2012

Nowadays, in metropolitan railroad, DC feeding system is being generally applied. In order to reduce damage of electro-chemical corrosion caused by stray current and leakage current, in DC feeding system, rail is used as negative-polarity return conductor for traction load current. However, it has problem of rail potential increase and there are no adequate measures to prevent it in domestic. The rise of rail potential leads to damage for human and equipments. To solve the problems, this paper presents fundamental theory and related standards about rail potential increase. And then, we analyzed field testing data and simulated a variety of operations by using PSCAD/EMTDC as an analysis program of power system. In addition, this paper suggests rail potential limit device and addresses how to the device. To verify the effect, simulation of DC feeding system before and after the application of the device is carried out in various cases.

• 전기학회논문지
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• 제64권10호
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• pp.1426-1431
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• 2015

Piezoelectric pump can be considered as R-C load and it needs something special driver because the output voltage does not become 0 even though the applied voltage is 0 with common converter. This operating system consists of fly-back converter to increase the input voltage and energy recovery inverter to apply square voltage to the piezoelectric pump. The energy recovery inverter can charge and discharge the energy of capacitive load. In this paper, to enhance performance of the driver, a few elements or circuits are added and modified. To drive the inverter safely, current limit resister is added and adjusted the value to valance the charging and discharging current. In addition, a current limit inductor is added to the input side to limit the input current and enhance the efficiency. Inductor only may make oscillation and another resister is added parallel to the inductor to solve this problem. The converter and inveter are assembled to one board for compactness. The appropriateness is proved with simulation and experiments.

• 한국항공운항학회지
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• 제27권4호
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• pp.105-113
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• 2019

The commercial pilot retirement age has continued to 65 since the International Civil Aviation Organization(ICAO) amended the recommended age limit from 60. The target of this review is to analyse whether aged pilots have an increased age-dependent risk of medical incapacitation. Medical in-flight incapacitation is actually very rare event and the demonstrated annual incapacitation rate provides an acceptable risk within the criteria known as 1% safety rule for a pilot undertaking air transport operations while some controversies exist. There is a possibility that the accident rate has decreased due to the improved skill by increasing pilot's age. At the decision of flight or not for elderly airline pilot the interacting factors of personal health status, piloting experience and new flight environments should be considered to define job limit criteria than mere the age. Results of a survey led by airline pilot association in Korea shows 65% of airline pilots are willing to fly without any age limit and 87% agreed that age limit is worthy to extend beyond current standard on the basis of medical examinations. Only 11% agreed to maintain current age limit.